Diastereomeric metallatetrahedron complexes of the type Re-2(AgPR3)(2)(mu-PCy2)(CO)(7)Z (R = Et and Ph; Z = (-)- and (+)-camphanate): synthesis, structure and CD data

Diastereomeric pairs of metallatetrahedron clusters of the type Re-2(AgPR3) (2)(mu-PCy2)(CO)(7)(ax-(+)/(-)-camph) ((+)-auxiliary, R=Ph 4a, 4b or Et: 6a , 6b and (-)-auxiliary, R=Ph 5a, 5b or R=Et: 7a, 7b) were prepared from the eta(1)-carboxylate substituted dirhenium salt Li[Re-2(mu-H)(mu-PCy2)(CO)(7 )(ax-eta(1)-(+)/(-)-camph)] (camph=camphanate) and less than stoichiometric amounts of [Ag(PR3)BF4] (R=Ph or Et) in solution at room temperature. The diastereomers were separated using PLC and identified by means of IR, H-1 a nd P-31 NMR, UV/VIS and CD spectroscopy. Using single crystal X-ray analysi s the molecular structure of 4a/4b in material I and 4a/5a in II have been determined to assign the absolute configuration of the clockwise (C) and an ticlockwise (A) configurated tetrahedral Re2Ag2 framework in a ligand spher e of C-1 symmetry. These are the first structures which show a chelate like co-ordination of the carboxylic group of the camphanate ligand in a hetero metallic cluster complex. Based on their CD spectra the absolute configurat ion of other chiral carboxylate substituted metallatetrahedra of the type R e-2(MPR3)(2)(mu-PCy2)(CO)(7)(ax-OC(O)R) (M=Au or Ag) can be assigned.